Mother's milk is recommended for all infants. However, in some cases breast feeding is inadequate or unsuccessful for medical reasons or the mother chooses not to breast feed. Infant formulas have been developed for these situations.
Immediately before birth, the gastro-intestinal tract of a baby is thought to be sterile. During the normal process of birth, it encounters bacteria from the digestive tract, skin and environment of the mother and starts to become colonized. The gut microbiota of infants is usually heterogeneous during the first few days of life, independent of feeding habits. However, during the months prior to weaning differences in the microbiota composition between breast-fed and formula-fed infants are apparent. These differences in the microbiota may partly explain the lower incidence of intestinal infection observed in breast-fed infants compared with formula-fed infants. In full-term infants, breast feeding induces the development of a microbiota rich in Bifidobacterium sp. Other anaerobes such as Clostridium sp. and Bacteroides sp. are more rarely isolated, and facultative anaerobes such as Escherichia sp. and enterococci are even less numerous. In contrast to breast-fed infants, formula-fed infants are often colonized by a more diverse microbiota including Clostridium perfringens, Escherichia coli and Bacteroides in addition to bifidobacteria. After the completion of weaning, a pattern of gut microbiota that resembles the adult pattern becomes established.
The new generations of infant formulas are designed to mimic the health advantages of human milk. One approach is to attempt to modify the intestinal microbiota by supplementing formulas with components that are recognized to promote the proliferation of Bifidobacteria. For example, research into the composition of human milk and the way this changes over the period of lactation suggests that the type and concentration of protein in human milk are likely to affect the gut microbiota, and changing these parameters in formulas may improve their bifidogenic properties.
Breast-fed infants are better protected against infections of the GI, respiratory, and urinary tracts as well as other diseases compared with those who are formula-fed (Cleary T. D. “Human milk protective mechanisms” Adv Exp Med Biol 2004; 554:145-54). Salminen and co-workers have attributed this effect at least partly to differences in microbiota composition (Salminen S. J., Gueimonde M., Isolauri E., “Probiotics that modify disease risk”. J Nutr 2005; 135:1294-8).
Further, it has been suggested that aberrant colonization of the infant gut may have specific consequences in terms of the subsequent development of the infant. For example, Laitinen et al found that failure to establish an early bifidogenic microflora may be an additional risk factor for wheezing and allergic sensitization to food allergens (Laitinen et al “Evaluation of diet and growth in children with and without atopic eczema: follow-up study from birth to four years” Brit J Nutr 2005; 94: 565-74). It has also been suggested that systemic low-grade inflammation and a sub-optimal gut microbiota may be implicated in the development of obesity (Fantuzzi G. “Adipose tissue, adipokines, and inflammation” J Allergy Clin Immunol. 2005; 115:911-919, Bäckhed F, Ding H, Wang T, et al. “The gut microbiota as an environmental factor that regulates fat storage” Proc Natl Acad Sci USA. 2004; 101:15718-15723).
Given the characteristic gut microbiota of breast-fed infants and the associated health benefits such as protection against infections, there is a real need to develop formulas with similar properties to human milk to ensure that infants who cannot be breast-fed obtain at least some of the beneficial effects conferred by human milk.